I recently put on a rebuilt carb from a friend. The carb is a 650cfm holley double pumper that has been jetted to a 780cfm (was what i was told). The car is a rocket until the mechanical secondaries are opened, then it boggs down and sems to loose its power. The Carb is on a 69 396/265hp engine which is hopped up with an agressive cam and other add on's (not sure what exactly)the intake is an older Holley Street Dominator single plane, open plenum alum. intake for a Spread Bore...yes a spread bore. I have a carb adapter. Also the timing on the dual point Accell distributor was advanced. What could be causing this problem??? Too much fuel? Any help will be greatly appreciated.

P.S. I just became a Team Chevelle Member tonight!!!

Originally posted by marilynSS396:
I recently put on a rebuilt carb from a friend. The carb is a 650cfm holley double pumper that has been jetted to a 780cfm (was what i was told). The car is a rocket until the mechanical secondaries are opened, then it boggs down and sems to loose its power.
P.S. I just became a Team Chevelle Member tonight!!! marilynss396,

The term "650 jetted to a 780" is a misnomer. The 650 will still flow 650 cfm. Now you have too much fuel. Go back to the stock specs on that carb and give it a run. It should run great, maybe a teeny bit limited at the higher RPMs.

The other probem is that single plane intake, and the adapter. Don't know what axle ratio or trans you have, but generally a dual plane is best for the street. Avoid adapters if you can.

Once you put the original jets in and bolt on a dual plane intake you should find it runs MUCH better!

Mike

Uncle is correct CFM (Cubic Feet per Minute)refers to air flow not fuel.

Welcome to a great site. I learn something just about every time I check it.
With your air cleaner off(engine not running) work the throttle linkage and check the delivery on the secondary accelerator pump. Take the sight plug out of the secondary float bowl and make sure it's got fuel in it, it could have trash in the needle and seat and be empty.
Howard, Miami

An adapter on an open plenum/single plane intake is not a problem..now if you had a square bore carb going on a stock q-jet/spreadbore dual pane intake,that would be a problem.An yes,there is no way to make a 650 "flow" to 780 or whatever.
I'd check your secondary float level.Check your secondary accelerator pump shot too.It could be a case of too much gas or not enough.

I Have noticed that my secondary accelerator pump was not working. The intake is for a spreadbore and the carb is a squarebore but i have a spreadbore to squarebore adapter. Mike my axle ratio is 3.73:1 tranny is a Muncie 21

Get Rid of that single plane and go dual I have a very agerssive cam and did so myself.Uncle is right about the jets check our post in the here and performance section there are some good articals on holley setup.Don't cut corners and do like it says take the carb off the car set everything up on it and recheck floats with the engine warm.Check the carb number and one of us will check the book to give you jets# and whatever you need.

This will give you a good starting point!!

[QUOTE]Originally posted by marilynSS396:
[QB] I Have noticed that my secondary accelerator pump was not working /[QUOTE]

Then that is the problem.Your adapter is fine.Yes,a dual plane would benefit your combo,but for now,you need to get that secondary accelerator pump straightened out.

I replaced the accelerator pump diaphrams when i got the carb(both diaphrams) Maybe i screwed it up somehow. Will an inoporative Acel. pump cause continuous bogging?

Originally posted by marilynSS396:
I replaced the accelerator pump diaphrams when i got the carb(both diaphrams) Maybe i screwed it up somehow. Will an inoporative Acel. pump cause continuous bogging? Hey neighbor. smile.gif The secondary accelerator pump's function it to prevent bog as the secondaries open. I think you're on the right track. ;)

Originally posted by marilynSS396:
I replaced the accelerator pump diaphrams when i got the carb(both diaphrams) Maybe i screwed it up somehow. Will an inoporative Acel. pump cause continuous bogging? The accelerator pump is needed WHILE the transistion from part throttle to WOT is occuring. I would assume that the shot from the pump is used up after a second or so. Any bogging after that would indicate a calibration problem. In summation, if the bog continues to occur after you get the accelerator pumps working you need to look at the carb calibration itself.

Mike